In the field of semiconductor manufacturing, it has been recognized since the beginning of the industry that removing particles from semiconductor wafers during the manufacturing process is a critical requirement to producing quality profitable wafers. While many different systems and methods have been developed over the years to remove particles from semiconductor wafers, many of these systems and methods are undesirable because they cause damage to the wafers. Thus, the removal of particles from wafers must be balanced against the amount of damage caused to the wafers by the cleaning method and/or system.
Existing techniques for freeing the particles from the surface of a semiconductor wafer utilize a combination of chemical and mechanical processes. One typical cleaning chemistry used in the art is standard clean 1 (“SC1”), which is a mixture of ammonium hydroxide, hydrogen peroxide, and water. SC1 oxidizes and etches the surface of the wafer. This etching process, known as undercutting, reduces the physical contact area to which the particle binds to the surface, thus facilitating removal. However, a mechanical process is still required to actually remove the particle from the wafer surface.
For larger particles and for larger devices, scrubbers have been used to physically brush the particle off the surface of the wafer. However, as devices have shrunk in size, scrubbers and other forms of physical cleaners have become inadequate because their physical contact with the wafers causes catastrophic damage to smaller devices.
The application of acoustic energy during wet processing has gained widespread acceptance to effectuate particle removal, especially to clean sub-micron particles off wafers (or other flat articles) undergoing fabrication in the semiconductor process line. The application of acoustic energy to substrates has proven to be a very effective way to remove particles and to improve the efficiency of other process steps, but as with any mechanical process, damage to the substrates and devices thereon is still possible. Thus, a need exists for a cleaning apparatus or system that can break particles free from the delicate surfaces of a semiconductor wafer without damaging the device structure and while enhancing cleaning uniformity.